Small Engines (Lawn Mowers, etc.): weed whacker and roto tiller woes..., roto tiller, intake leak

Question
Hi,
I'm through with guessing about how to fix the small engines. Here it is... I have a roto tiller about 5 yrs old. Model #21A-342-062 31138 serial #1A269K50384. Family VBS205U1G1RA:EM displacement 190cc model 11HOHV 95-98 california emission regs for ULGE engines. The darn thing ran great when it suddenly stopped. I realized it was a broken valve spring. Then after replacing them, it ran great again for a few minutes then stopped. Now I am unsure what it is. It is getting spark. It shoots fire out the carb and muffler port, but won't catch. I sprayed carb cleaner, but doesn't help. Also for the second problem. A Snapper S31SST 17 inch 31cc engine weed whacker. It has not run since I had it. I pulled the coil, in efforts to get good spark, and replaced that. No good. It has fuel that I can see and I pulled the carb numerous times and doused it w/ carb cleaner and poked all holes I could. It rotates great with the cord and sounds like it has compression, but will not spit in the least bit to make a start. It just turns, no fire. Both of these are really trying my patience now. Can you give me some ideas as to what these darn things are doing...or not doing?
Thank you.

Answer
Mike
For the tiller when the valve spring broke did you change both springs and valves? You should have as now one spring is stronger than the other causing it to open or close tighter than the old one. You should have put in two new valves springs and ground down the seats.

try these out  
Possible causes:

Carburetor set too lean.
Magneto is not timed correctly.
Valves are sticking.

As far as the weed whacker sounds like you have a intake leak somewhere on or around the intake gaskets, Make sure they are all in place check your user manuals for the parts list.